(A) Field of the Invention
The present invention relates to an electrode structure and light-emitting devices using the same, and more particularly, to an electrode structure with parallel-connected electrodes configured to prevent the light-emitting device from overheating by eliminating the current-crowding phenomenon so as to dramatically improve the reliability of the light-emitting device.
(B) Description of the Related Art
Semiconductor light-emitting devices such as light-emitting diodes (LED) are widely used in traffic lights, vehicle electronics, LCD backing lights, and general illumination. In the light-emitting diode an n-type semiconductor layer, a light-emitting region and a p-type semiconductor layer are essentially made to grow on a substrate to form a layered structure, and the electrodes are formed on the p-type semiconductor layer and on the n-type semiconductor layer. Light is generated through the recombination of holes and electrons that have been injected through the semiconductor layers to the light-emitting region, and then emitted through a light transmitting electrode on the p-type semiconductor layer or from the substrate. The material used for preparing the visible light-emitting diode includes the III-V compound such as AlGaInP for green, yellow, orange or red light-emitting diodes, and GaN for blue or ultraviolet light-emitting diodes, wherein the GaN light-emitting diode is formed on the sapphire substrate.
FIG. 1 illustrates a top view of a nitride light-emitting device 30 according to the prior art, and FIG. 2 illustrates a cross-sectional view of the nitride light-emitting device 30 according to the prior art. The nitride light-emitting device 30 according to the prior art includes a sapphire substrate 32, an n-type nitride semiconductor layer 34, a light-emitting layer 36, a p-type nitride semiconductor layer 38, a contact layer 40, a p-type electrode 42, and an n-type electrode 44. The n-type electrode 44 is formed on the top surface of the n-type nitride semiconductor layer 34, and the p-type electrode 42 is formed on the top surface of the contact layer 44.
The nitride light-emitting device 30 suffers from a current-crowing problem, i.e., the current is not distributed uniformly between the n-type electrode 44 and the p-type electrode 42, and concentrates at a local region 46 of the light-emitting layer 36 in close proximity to the n-type electrode 44. This current-crowding problem not only increases the forward biasing voltage of the light-emitting diode, but also reduces the light-emitting efficiency of the light-emitting layer 36 at the side distant from the n-type electrode 44, which decreases the overall brightness of the light-emitting device 30. In addition, progressively accumulating heat in the local region 46 causes the overheating phenomenon, which dramatically decreases the reliability of the light-emitting diode.
FIG. 3 and FIG. 4 illustrate a light-emitting diode array disclosed in US 2005/0224822. The preparation of the light-emitting diode array includes forming a depression by etching, filling dielectric material 17 into the depression to divide the light-emitting stack consisting of a first type semiconductor 14, a light-emitting layer 15 and a second type semiconductor layer 16 into a plurality of light-emitting diodes 1a and 1b, and connecting the first electrode 18 and the second electrode 19 of the adjacent light-emitting diodes 1a and 1b in series to form the series-connected light-emitting diode array, as shown in FIG. 4.